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2 INPUTS FOR ST3 PLAN
This chapter discusses the specific input data and assumptions used to perform staged forecasting analysis
in support of the ST3 System Plan. Key input data assumptions include Current Year (2014) and Future
Year (2040) staged forecasting analyses developed from the validated 2014 transit-trip tables. These
forecasts include, in three stages, the separate effects of changes due to:
 Population and employment forecasts provided by the Puget Sound Regional Council (PSRC)
 Highway congestion, automobile operating costs, parking costs, and median income forecasts
based on available PSRC model databases
 Transit service levels and speeds assumed for the ST3 System Plan
The assumptions and input data used to produce Current Year and Future Year ridership forecasts are
described in the following sections.

2.1 PSRC Demographic Forecasts
PSRC concluded an update of regional land use forecasts and released a set of forecasts through the year
2040 in January 2016 referred to by PSRC as a Land Use Vision (LUV.1) forecast.
Table 2-1 presents district-level 2014 and 2040 households, population, and employment for the four-
county PSRC region, with allocations to 27 summary districts. Figure 2-1 shows a map of the district
boundaries. The forecast growth rates between 2014 and 2040 in total regional households, population,
and employment (shown in Table 2-1) are, respectively, 1.40, 1.27, and 1.45.
Details on the methods and review processes used in the development of demographic forecasts are
provided in the PSRC Land Use Vision document dated January 14, 2016.

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2.2 Non-transit Inputs and Assumptions
2.2.1 Highway Congestion
The current version of the PSRC model adopted by the Washington State Department of Transportation
(WSDOT) for performing detailed travel and toll forecasting in support of major capital projects was used
to produce peak and off-peak highway travel times.
The background (baseline) highway network assumed in the WSDOT model included financially
committed highway projects. Base year 2014 and future year 2040 highway networks within the Sound
Transit District were examined and further refined to better reflect the current highway network and its
performance. Subsequently, PSRC model runs were performed to produce peak and off-peak highway
travel times required for the 2040 Stage 2 ridership forecasting analyses.
In addition, PSRC model databases were used to develop arterial and freeway speed degradation rates
required for 2040 transit speed analysis. These speed degradation estimates are based on a method agreed
upon between Sound Transit and the Federal Transit Administration (FTA).
2.2.2 Parking Costs
For the purpose of representing daily and hourly parking costs in Stage 2 of the Sound Transit ridership
model, a survey of parking costs scattered around the larger downtown area was recently updated. Based
on the data from this survey, base year (2014) daily parking costs were updated, and 30 percent of daily
parking cost was used to represent off-peak parking costs in the Sound Transit model.
In the Sound Transit model, only the change in parking costs between 2014 and 2040 has any effect on
ridership. The change in zonal parking costs used in the Sound Transit model reflect a conservative annual
real growth in parking costs related directly to PSRC forecasts of increases in employment density.
2.2.3 Per-mile Vehicle Pricing
Automobile operating costs for travel demand models are expressed in cents-per-mile. Typically, the costs
include most of the out-of-pocket costs of driving a car but none of the ownership costs. Automobile
operating costs for these forecasts are assumed to be about 24 cents-per-mile in 2014 dollars.
For forecasting 2040 transit ridership, the Sound Transit model includes an assumption of a slight increase
in driving costs, related to a PSRC assumption of per-mile road usage fees for all automobile travel in the
region by 2040. This assumption is consistent with PSRC’s Transportation 2040 plan. A letter from PSRC
to Sound Transit (October 21, 2015) describing this assumption is included in Appendix B.
Because the basic assumption is that the costs of driving will increase only slightly above the rate of
inflation, due to the per-mile road usage fees, this input has a small effect on the transit ridership
forecasts.
2.2.4 Effects of Regional Income Increase
PSRC does not forecast household income at the zonal level. Therefore, the Sound Transit ridership
model only considers forecasts of a future change in regional median household income. Currently, the
Sound Transit model assumes real growth in income at 1 percent per year. This is consistent with the
long-term historical rate of real growth in income in the Puget Sound region and has a tendency to slightly
lower estimates of future ridership as median income increases.

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2.3 Transit Service Inputs and Assumptions
2.3.1 Transit Fares
In all model applications to date, fares have been assumed to increase at the same rate as the overall rate
of inflation in the region. This is a policy assumption consistent with the local transit agencies’ practice of
periodically adjusting fares to keep up with inflation.
Transit fares for future years have been recently updated to reflect prevailing transit fares in 2015. Base
year 2014 and future year 2040 transit fares used in the Sound Transit model are identical.
2.3.2 Transit Service Levels
For the ST3 System Plan ridership forecasting, transit service levels are required for the Base Year 2014,
for a future Baseline scenario, and for an ST3 Build scenario. The future Baseline scenario reflects an
assumption of what transit service would exist if only the ST2 Sound Transit investments were in
operation (and not the ST3 investments). The future ST3 Build scenario reflects transit service assumed to
be in operation upon completion of the ST3 investments.
Background Bus Assumptions
In both future scenarios, the approximate future bus service hours for each operator are assumed to be
slightly higher than existing levels while also including implementation of proposed local bus rapid transit
projects. The operating funds for these transit service levels reflect each bus operator’s expectations of
revenue growth from existing sources and from potential funding partners. Sufficient real growth in
operating revenues is in all cases assumed to be at least sufficient to operate existing levels of service, even
if operating speeds decline over time.
For both the Baseline scenario and the ST3 Build scenario, local service is adjusted to serve the rail lines
according to input from the bus operators, including their long-range plans. Since neither Pierce Transit
nor Community Transit expect to provide long-distance express bus service into King County, Sound
Transit is assumed to be the sole provider of inter-county express service by 2040, via ST Express bus,
Sounder commuter rail, or Link light rail. This basic assumption is applied to both the Baseline and ST3
Build scenarios.
Appendix A provides further detail on bus assumptions.
Baseline Link Rail Operation
Service levels on Link for a Baseline scenario were equilibrated to 2040 Baseline demand levels. These
demand levels require 6.5-minute peak headways on each of the two assumed Link operating lines. The
two Link operating lines assumed were
 Kent/Des Moines to Lynnwood via the existing Downtown Seattle Transit Tunnel (DSTT)
 Redmond Technology Center to Lynnwood via the existing DSTT
The ridership forecasts assumed a 10-minute off-peak policy headway on all Link lines.
On Tacoma Link, the ST3 Baseline assumed 10-minute headways for both peak and off-peak periods.
Future Baseline peak-direction service levels on Sounder were assumed to be 10 trains per peak on the
South line and 4 trains per peak on the North line.

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ST3 Plan Rail and Bus Rapid Transit Operation
The following four Link operating lines were assumed for the ST3 Plan:
 West Seattle to Everett via the existing DSTT
 Redmond to 128th SW (Mariner Park and Ride) via the existing DSTT
 Ballard to Tacoma via a new downtown Seattle rail tunnel
 South Kirkland to Issaquah via the downtown Bellevue rail tunnel
For ridership analysis, future service levels on Link for an ST3 Build scenario were equilibrated to 2040
ST3 Build demand levels. These require 6-minute peak headways on each of the three assumed Link
operating lines that directly serve downtown Seattle. Peak service levels on the South Kirkland to Issaquah
line were also assumed at 6-minute headways due to the assumed joint use of the downtown Bellevue rail
tunnel.
For ridership analysis, the assumed future off-peak service levels on all four of these lines were policy-
determined headways of 10 minutes.
On Tacoma Link, the ST3 System Plan assumed 6-minute peak headways, and 10-minute policy-
determined off-peak headways.
Future ST3 System Plan peak-direction service levels on Sounder were assumed to be 10 trains per peak
on the South line and 4 trains per peak on the North line. No assumptions were made about off-peak
Sounder service.
For ridership analysis, the future service levels on the two proposed BRT lines were policy-determined
headways of 10 minutes for peak period and 15 minutes for off-peak period.

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3 BUILD-UP ANALYSIS
3.1 Build-up Summary Results by Stages
As discussed in detail in Chapter 2 of the Transit Ridership Forecasting Methodology Report (September 2016), the
Sound Transit patronage forecasting is performed in three separate stages. This process distinguishes and
facilitates the evaluation of incremental changes to regional population and employment, changes to
highway times and costs, and changes to transit service.
Because the Current Year estimates for the ST3 System Plan are not actually forecasts, a build-up analysis
would not be very illuminating for these Current Year estimates, although it is very important for future
years. Therefore, this section on build-up analysis only addresses the Future Year 2040 forecast.
In Stage 1, implied growth in the Land Use Vision forecasts at the forecasting analysis zonal level prepared
by PSRC are used to grow base-year transit demand from a base year to a forecast year. In Stage 2 of the
Sound Transit modeling process, the influence of changes in highway congestion, auto operating costs,
parking costs, and income are incorporated. Changes in transit service levels and fares are considered in
Stage 3. The staged forecasting analysis results for Future Year PM peak period and daily ridership are
summarized at 27 districts in Table 3-1, Table 3-2, and Table 3-3. A map of the 27 district boundaries is
shown in Figure 2-1.

3.2 Build-up Ridership Tables
The results of Stage 1 of the forecasting analysis indicate that changes in regional demographics between
2014 and 2040 result in an increase of approximately 42 percent in total daily transit trips. Total
households and employment for the four-county region are projected to increase by 40 and 45 percent,
respectively, between 2014 and 2040. Overall growth in transit demand related to growth is balanced
between the overall employment growth rate and the overall household growth rate.
Within the Seattle central business district (CBD), employment is projected by PSRC to increase by
57 percent between 2014 and 2040, while CBD households are projected to increase by 135 percent,
reflecting continuation of the current trend of intense CBD residential development. Slightly higher
percentages of the forecast future employment growth occur away from traditional transit markets
(Table 2-1).
Table 3-1 shows the PM peak transit trip origins as they change through the staged incremental forecast.
For example, the Seattle CBD PM-peak transit origins in Stage 1 of the forecast are shown to increase
from 37,400 to 56,800. This is a growth of approximately 50 percent, closely reflecting the PSRC forecast
increase in CBD employment.
Table 3-2 shows the PM-peak transit trip destinations as they change through the staged incremental
forecast. For the same example, the Seattle CBD PM-peak transit destinations in Stage 1 of the forecast
are shown to increase from 6,100 to 11,300. This is a growth of approximately 85 percent, reflecting the
higher PSRC forecast increase in CBD households but softened somewhat by the more modest increase
in employment.
Table 3-3 shows the daily transit trip ends as they change through the staged incremental forecast. Off-
peak trips and daily trip totals are balanced between origins and destinations, so it is redundant to show
daily origins and daily destinations separately.

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In Stage 2 of the forecasts, the analysis considers the combined effect of changes in auto operating costs,
parking costs, highway congestion, and income, as discussed above in Section 3.1 and also in the Transit
Ridership Forecasting Methodology Report. In Table 3-1, Table 3-2, and Table 3-3, these Stage 2 ridership
changes result primarily from changes in parking costs, congestion and income. The percentage change in
2040 Stage 2 relative to Stage 1 is approximately 9 percent in the peak periods and 6 percent for total daily
transit trips.
In Stage 3 of the forecasting analysis, changes in transit service relative to the 2014 base are considered for
the ST3 System Plan. Similar changes in transit service are applied for both the Current Year (2014)
estimate and the Future Year (2040) forecast.
Note that Stage 3 reflects the net combined effect of changes in transit service levels, transit speeds, and
transit fares. Table 3-3 shows that for the 2040 Baseline scenario the improved transit service would
increase 2040 daily transit trips by approximately 24 percent relative to the 2040 Stage 2 forecasts.
This 24-percent increase is a regional total and reflects the combined effect of the Sound Move and ST2
investments. These other investments include, for example, the East Link project, the Northgate Link
Extension project, and some other projects not yet in service in 2014, such as the University Link project.
The net effect of ST3 investment increases Stage 3 daily transit trips by approximately 12 percent over
ST3 Baseline Stage 3 total daily transit trips.

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4 RIDERSHIP RESULTS
Regional transit Current Year (2014) ridership forecast results are shown for the Baseline scenario and the
ST3 System Plan, and Future Year (2040) forecasts are shown separately for these same scenarios. All
tables for the ST3 System Plan reflect results for the implementation of the entire plan. This provides a
range of ridership forecasts as suggested by the State auditor.
Presentation of two sets of ridership results are also consistent with the latest FTA policy guidelines for
New Starts projects. Sound Transit’s enabling legislation advises for project planning to follow forecasting
guidelines published by FTA for New Starts projects in order to increase the likelihood of future federal
funding.
The Current Year and Future Year estimates in the following system ridership tables are for ridership
within the Sound Transit district boundaries comprising the urbanized portions of Pierce, King, and
Snohomish counties. For this model, riders are considered to be within the district if either end of their
trip occurs within the district boundary.

4.1 Systemwide Ridership Results for Current Year and Future
Year
Table 4-1 and Table 4-2 contain the Current Year 2014 and Future Year 2040 daily and annual estimates
of transit travel within the Sound Transit District, respectively. Current Year estimates are unaffected by
forecasts of population and employment growth or by future traffic conditions, future parking costs,
future income levels, or any other external forecasting inputs.
The importance of the Current Year results in Table 4-1 and Table 4-2 is apparent. They show that if the
ST3 System Plan were in operation today, it would carry a substantial number of riders, most of whom
live in the ST3 corridors today and many of whom are already on transit.
The 2040 forecasts incorporate the PSRC LUV.1 forecasts as released in January 2016 and summarized in
Table 2-1. Chapter 3 above illustrates, via the build-up analysis, the relative importance of these PSRC
forecasts to transit ridership forecasts for future years.
Although the Future Year forecasts also incorporate the effects on transit from changes in auto travel
costs and times, the difference between the Current Year 2014 estimates and the Future Year 2040
forecasts is primarily the PSRC demographic forecast. The difference is simple and direct and may be
easily traced from the demographic growth forecasts to the results.
Current Year and 2040 “New Riders” are the subtraction of the regional total transit trips in the Baseline
scenario from the ST3 System Plan regional total. This effectively represents an estimate of the travelers
who would shift from automobiles to transit solely due to the System Plan investments.
For 2040, the difference between the ST3 System Plan scenario and the Baseline scenario is a range of
56,000 to 72,000 daily transit trips. The midpoint of this range is 64,000 daily riders shifted, or about 20
million annual trips removed from highways.
For both the Current Year estimates and the Future Year 2040 forecasts in Table 4-1 and Table 4-2, the
final row shows the vehicle miles traveled (VMT) savings, which is an important input for calculation of
environmental benefits in FTA New Starts project evaluations. The four categories used by FTA are air
quality, energy use, greenhouse gas emissions, and safety. FTA monetizes the changes in these factors
which are attributed to the VMT reduction associated with the project.

described in detail in the Final Interim Policy Guidance—FTA Capital Investment Program (August 2015).
2For the year 2014, actual boardings are presented.

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Table 4-2. Systemwide Annual Transit Ridership Estimates, Current Year (2014) and 2040
Current Year (2014) 2040
without with without with
2014 ST3 Plan ST3 Plan ST3 Plan ST3 Plan
Total Transit Trips 117 million 145 million 158 million 183–221 million 202–245 million
New Riders / Switched to Transit (reduction in auto NA NA 13 million NA 19–24 million
trips)1
Total Transit Boardings 169 million 238 million 267 million 297–356 million 338–409 million
ST Boardings2
Link (excluding South Kirkland to Issaquah and 11 million 74 million 109 million 94–113 million 141–173 million
Tacoma Link)
Link (South Kirkland to Issaquah) NA NA 2 million NA 4–5 million
Link (Tacoma Link) 1 million 2 million 5 million 3–5 million 7–10 million
Total Link 11.9 million 76 million 116 million 97–118 million 152–188 million
Sounder 3.4 million 6 million 6 million 9–12 million 8–11 million
Sound Transit Bus Rapid Transit NA NA 6 million NA 7–9 million
ST Express Bus 17.7 million 15 million 7 million 19–23 million 9–10 million
Passenger Miles
Regional Total 1,073 million 1,510 million 1,745 million 1,930–2,350 million 2,276–2,808 million
Link 75 million 629 million 1,025 million 808–987 million 1,380–1,735 million
% on Link 6% 40% 57% 40% 59%
All ST Services 416 million 908 million 1,262 million 1,208–1,508 million 1,700–2,139 million
% on all ST services 39% 60% 72% 63% 75%
Savings in Vehicle Miles Traveled (switched to transit)
Regional Totals1 NA NA 216 million NA 314–411 million
1These two measures use the method required by the Federal Transit Administration (FTA) for estimating environmental and congestion relief benefits for FTA New Starts funding applications. They are

described in detail in the Final Interim Policy Guidance—FTA Capital Investment Program (August 2015).
2For the year 2014, actual boardings are presented.

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4.2 Project Ridership by Corridor
Table 4-3 details transit ridership by project. These ridership totals show ridership as trips-on-project,
following an FTA definition required in New Starts project evaluation. The definition basically counts all
transit trips that would, on an average weekday, use at least a portion of the project described. These
ridership numbers are developed both for the Current Year as a single estimate and for the Future Year as
a range. As mentioned above, all Current Year measures are estimates of ridership on a project as if the
project were currently in service.
The FTA definition of trips-on-project was extended for a bundle of projects under a system plan.
Estimates of trips-on-project, as shown in Table 4-3, reflect the summation of all of the trips on the
various projects.The cost-effectiveness measure shown in Appendix C to the ST3 System Plan is a
summation of transit trips using any segment of the ST3 Plan and does not double-count riders who use
more than one segment, whereas a summation of the riders of the bundled projects shown in Table 4-3
would result in double-counting of trips that use multiple ST3 segments.

4.3 Daily Volumes—ST3 Plan
Future Year (2040 midpoint) daily transit passenger volumes for the ST3 System Plan projects are
presented in this section.
The maximum load segments for the ST3 System Plan are the segments between Northgate and Beacon
Hill, with especially high passenger volumes through downtown Seattle. The daily north-south Link
volume is about 200,000 through downtown Seattle. Highest daily volumes outside downtown Seattle
occur, as expected, near the center of the system. Highest volumes occur at

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 North line: 148,000 between Westlake and Capitol Hill stations and 132,000 between UW and
University District stations
 East line: 70,000 between International District and Judkins Park stations
 South line: 86,000 between SoDo and Beacon Hill stations
 Tacoma Link: 20,000 through downtown Tacoma
 Sounder: 27,000 between Tukwila and Kent
Other daily passenger volumes on a few representative segments of Figure 4-1 include:
 North line: 82,000 just north of Northgate and 28,000 north of Ash Way
 Ballard line: 34,000 just west of Seattle Center
 West Seattle line: 32,000 on the West Seattle Bridge
 East line: 28,000 through the BelRed area east of downtown Bellevue
 Issaquah line: 12,000 between Bellevue and Factoria
 South line: 56,000 just south of the Airport and 26,000 south of Federal Way
The passenger volumes listed above and shown graphically in Figure 4-1 are not to be confused with other
ridership results presented above, such as project riders or forecast volumes, or counts presented in other
documents, such as daily station boardings. These passenger volumes are estimates of passengers passing
through various locations in a system.

 ST3 Build Network (ST3 Plan)
SUMMARY
For the ST3 System Plan ridership forecasts, the background bus networks have been updated to reflect a
Sound Transit Express bus network as outlined by Sound Transit specifically for the ST3 investment
package for both a baseline scenario and a Build ST3 scenario.
The background bus networks were also updated to reflect the latest mid-range changes under considera-
tion by Community Transit (CT), Everett Transit (ET), Pierce Transit (PT), and King County Metro
(KCM). Sound Transit coordination with bus operators throughout the ST3 planning process provided
guidelines for long-range bus assumptions related to the ST3 rail extensions. This resulted in use of the
following assumptions for the background bus network for the ST3 Baseline and ST3 Plan scenarios:
 CT would delete service to King County, spending the savings on local service that intersects with
the light rail line and on an expanded Swift BRT network
 ET would not need to make any significant changes related to a rail extension from Lynnwood to
Everett via Paine Field
 PT would likewise not need to make any changes to its local bus network due to the extension of
the south corridor light rail to Tacoma, the extension of Tacoma Link to Tacoma Community
College, or the extension of Sounder service to DuPont
For KCM, changes are related to the METRO CONNECTS concept networks developed by KCM in
2015–2016 as part of a long-range planning effort. The ST3 Baseline scenario is similar to the 2025
concept network, and the ST3 Plan scenario is similar to the 2040 concept network.
The Sound Transit Express bus networks for Baseline and Build scenarios are similar to the existing bus
network, though reflecting changes due to light rail extensions under each scenario. Corridors with rail
extensions generally have reductions in line haul parallel bus service with any savings reinvested either in
feeder service to rail stations or in non-rail corridors, as shown in Figure A-1. In all three corridors (north,
east, and south), ST Express routes would no longer duplicate rail service to downtown Seattle for both a
Baseline scenario and an ST3 Build scenario.

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ST3 BASELINE NETWORK
The Baseline background rail network reflects completion of the ST2 light rail network to Lynnwood,
Kent/Des Moines, and Redmond Technology Center and the current Sounder lines north to Everett and
south to Lakewood.
The ST Express network was updated to reflect some key changes from previous assumptions related to
the ST2 rail network:
 Truncation of ST Express services from Tacoma at Kent/Des Moines Station, except for ST 595
 Higher service investments between Issaquah and Bellevue, Redmond and the University District,
and Bothell/Woodinville and North Seattle
Relative to earlier Baseline networks, this network reflects some KCM-related changes. The 2025 network
from KCM was used to identify changes for their services in the Baseline network. Key changes included:
 Updated central and northeast Seattle networks, reflecting the University Link service integration
as implemented in 2016, and changes associated with the Northgate and Lynnwood Link
Extensions
 Modest headway changes to bus routes in the Kirkland area, reducing SR 520 bus volumes and
increasing local service in and between Kirkland Bellevue and Redmond
 Improved south King County service in and between Renton, Kent, and Auburn
 Modification to seven Rapid Ride routes in Seattle

ST3 BUILD NETWORK
The Build network adds modifications to the ST3 Baseline network described above, with network
changes based on light rail and bus rapid transit investments.
For ST Express, the Build network removes all bus service between Tacoma and Kent/Des Moines
(except for ST 595), between Everett and Lynnwood, and between Bellevue and Burien/Lynnwood—
each of these bus service reductions is dependent on replacement HCT service. This allows for a
reallocation of ST Express bus service hours to corridors not directly served by light rail or bus rapid
transit. Likewise, the Sounder extension to DuPont enabled the deletion of the ST Express bus service to
DuPont.
No significant changes were necessary for ET, CT, or PT local bus services due to light rail extensions to
Everett and Tacoma in the ST3 Build scenario. This includes even the CT Swift BRT routes, which have
all been planned assuming an eventual light rail extension to Everett.
KCM bus changes were focused on three key areas, targeting route modifications and new frequent routes
that provide local connections while also serving light rail stations:
 Ballard—Existing services between northwest Seattle and downtown were reduced or eliminated
to provide frequent connections on several routes within Ballard and adjacent neighborhoods.
 West Seattle—Existing services between West Seattle and downtown were reduced or eliminated
to provide frequent connections on several routes within West Seattle and to Burien and the
Duwamish industrial area.
 Federal Way—Some express service was reduced and reinvested in local connections in the
Federal Way and Auburn areas.